Pen holder



FIG. 1 is a right-hand perpsective view, showing the pen holder of my new design;

FIG. 2 is a front view thereof, the rear, left and right side views all being identical thereto;

FIG. 3 is a top view thereof; and,

FIG. 4 is a bottom view thereof. 

The ornamental design for a pen holder, as shown and described. 